1. Field of the Invention
The present invention relates to a method for determining an incident angle in measurement of a refractive index and a thickness.
2. Description of the Related Art
An ellipsometry is known as a method for measuring a refractive index of a thin film and the thickness thereof.
In the ellipsometry, a measuring operation of high accuracy is performed, but there is a case in which the accuracy is greatly reduced with respect to a certain measured film. It is possible to avoid a region reducing the accuracy by changing an incident angle. However, it is impossible to know in advance which incident angle should be selected to obtain a preferable accuracy in measurement. Therefore, it is necessary to calculate a suitable incident angle by a method of trial and error.
Accordingly, the inventor of this application proposed a method of specifying the incident angle at which the accuracy in measurement is deteriorated in advance in Japanese Patent Application No. 62-192396. However, this method is applied to only the measurement of the refractive index and the thickness with respect to a single layer film formed on a substrate having a known complex refractive index. Further, a light used in the measurement is limited to an S-polarized light.